The invention relates to an airbag rear suspension system for motorcycles. The invention allows a motorcycle operator to adjust the ride height of a motorcycle by varying the pressure in an airbag that replaces the stock coil-over shock absorber mechanism, providing substantial ride height adjustment for motorcycles equipped with modem swingarm-type rear suspension. The airbag suspension system is useful, for example, for touring motorcycles, which perform under a wide range of passenger and cargo loads, and for cruisers and show bikes, which are often raised or lowered for cosmetic reasons.
The combination of an internal combustion engine with a bicycle frame gave rise to the motorcycle around the turn of the 20th century. Initially, pneumatic tires and sprung saddles provided the only insulation from unwanted road vibrations. As motorcycle horsepower and speed increased, some form of front suspension soon became essential not only for rider comfort but for maintaining effective wheel-to-road surface contact. By comparison, motorcycle rear suspension was adopted slowly, particularly among American-based motorcycle manufacturers such as Harley-Davidson and Indian. To this day, xe2x80x9chardtailxe2x80x9d frames (i.e., frames that accept a rear wheel directly without the imposition of a suspension mechanism) are commonly used as the basis for custom xe2x80x9cchoppers,xe2x80x9d usually comprising Harley-Davidson drivetrains.
By the late 1950s, telescopic front forks and twin-shock absorber, swingarm-type rear suspension had become fairly standard on British and European motorcycles. In fact, the Norton xe2x80x9cFeatherbedxe2x80x9d frame, fitted with a tubular steel swingarm (along with ROADHOLDER(copyright) forks), is still highly sought after as the basis for custom xe2x80x9ccafxc3xa9 racersxe2x80x9d and Tritons (hybrid motorcycles with Norton frames and Triumph engines).
Since the mid-1980s, single rear shock absorbers have largely replaced twin rear shocks, especially on high-performance motorcycles. Single large shock units generally offer superior performance and greater adjustability than two relatively small shocks. Perhaps largely as a consequence of having to mount the single shock near the pivot-point of the swingarm to avoid interference with the rear wheel, most modern swingarm rear suspension designs incorporate a relay arm through which the shock is connected to the swingarm. The relay arm amplifies the travel of the swingarm, often in a progressive manner, allowing the use of lighter coil springs and avoiding the undesirable situation where a shock absorber must dampen the action of a heavy spring while operating within a short range of travel.
Modern rear shock absorbers, particularly aftermarket performance shocks, are frequently adjustable for spring preload, compression damping, and rebound damping. In some cases, ride height is also adjustable but usually involves detaching the bottom end of the shock from the relay arm to either elongate the shock absorber or adjust the height of the bottom shock mounting point. This type of adjustment requires that the rear wheel be completely unloaded and is not readily performed without appropriate lifting equipment and mechanical aptitude. Moreover, most motorcycle suspensions are not adjustable for ride height.
Many modern cruisers and touring motorcycles feature single-shock, swingarm rear suspension. Since these motorcycles are routinely ridden for long distances, over variable road surfaces, and are often fully loaded with a passenger and gear, the ability to quickly and easily vary ride height is particularly desirable. To this end, the airbag suspension system of the instant invention allows a motorcycle operator to adjust ride height to accommodate different loads, to change the handling characteristics of the motorcycle, or to alter the appearance of the motorcycle.
Motorcycle airbag rear suspensions have been described in U.S. Pat. No. 6,003,628 (Dec. 21, 1999; herein the ""628 patent), U.S. Pat. No. 6,193,005; (Feb. 27, 2001 herein the ""005 patent), and U.S. Pat. No. 6,357,546 (Mar. 19, 2002; herein the ""546 patent); however, these suspension systems are specifically designed for Harley-Davidson SOFTAIL(copyright) rear suspension. The SOFTAIL(copyright) frame and swingarm are designed to mimic the appearance of traditional Harley-Davidson hardtail frames. As a result of design constraints imposed by the desire to conceal the rear suspension mechanism, the SOFTAIL(copyright) suspension system utilizes an unusual spring and shock absorber arrangement wherein a pair of coil-over shocks are positions under the frame in front of the swingarm. Unlike the shock absorber assemblies of virtually all other motorcycles which compress when the swingarm rises (i.e., the suspension compresses), the SOFTAIL(copyright) coil-over shock units extent when the swingarm rises.
As a consequence of this unorthodox design, airbag devices are not readily compatible with the SOFTAIL(copyright) suspension system. Accordingly, an essential element of the ""628 and ""005 suspension systems is an elaborate sliding housing mechanism that translates the extending or pulling motion of the SOFTAIL(copyright) suspension into a compressing or pushing motion. In contrast, the airbag component of the instant invention is positioned within the included angle of the rear suspension where it is properly situated to be compressed in response to a rising swingarm.
The airbag suspension system described in the ""546 patent also features a device to translate the extending or pulling motion of the SOFTAIL(copyright) suspension to a compressing motion for use with an airbag devise. In this case, the invention comprises a pair of pivotally connected plates that share a common pivot axis with the stock SOFTAIL(copyright) swingarm and main frame. The lower section of one plate connects to a shock absorber mounted in the conventional SOFTAIL(copyright) shock location. The upper part of the pivoting plates accept an airbag, essentially extending the SOFTAIL(copyright) suspension above the swingarm-frame axis to resemble a more modern swingarm suspension system.
The pivoting plate and airbag assembly of the ""546 patent is not applicable to a modern swingarm suspension system that already comprises a mechanism for compressing a spring (or an airbag device). Moreover, there is usually no free space to insert an additional pivoting device between the swingarm pivot points (refer to FIG. 1), particularly on motorcycles that feature swingarms comprising single-piece, lateral box section members that house both sets of swingarm bushings or bearings. For these and other reasons, the suspension systems of the ""546, ""628, and ""005 patents are narrowly tailored to suit the unorthodox SOFTAIL(copyright) suspension system.
The instant invention satisfies a need in the field of motorcycling by providing an airbag suspension system that can be fitted to motorcycles with modem swingarm-type rear suspension. The airbag suspension system of the invention provides adjustable ride height for varying loads, for rider and passenger comfort, or for appearances, with ride height being adjustable while the motorcycle is in motion.
The instant invention is drawn to an airbag suspension system for motorcycles having a main frame and a swingarm-mounted rear wheel. In the most simple embodiment of the invention, the airbag suspension system comprises:
a) an upper airbag mount having a main frame attachment site, an upper airbag attachment site, and a shock mounting site, the upper airbag mount being attached to the main frame at the main frame attachment site,
b) a lower airbag mount having a swingarm attachment site and a lower airbag attachment site, the lower airbag mount being attached to the swingarm at the swingarm attachment site,
c) an inflatable airbag having a longitudinal axis along which the airbag changes length upon inflation, and having an airbag mount attachment site at each end of the longitudinal axis, the airbag being attached to the upper airbag attachment site and the lower airbag attachment site;
d) a relay arm having a main frame attachment site at a first end, a shock absorber attachment site at a second end, and a tie-rod attachment site between the first and second ends, the relay arm being pivotally attached to a relay arm mounting site on the main frame,
e) the relay arm additionally pivotally attached at the shock absorber attachment site to a first end of a shock absorber,
f) a second end of the shock absorber being pivotally attached to the upper airbag mount shock mounting site,
g) the relay arm being additionally pivotally attached at the tie-rod attachment site to a first end of at least one tie-rod,
h) a second end of the tie-rod being pivotally attached to a tie-rod mounting site on the swingarm.
In a preferred embodiment of the invention, the upper airbag mount is fixedly attached to the main frame at the main frame attachment site. In another embodiment of the invention, the upper airbag mount is pivotally attached to the main frame at the main frame attachment site. In yet another embodiment of the invention, the upper airbag mount comprises multiple frame attachment sites. The upper airbag mount may be attached to the main frame by one or more methods, including but not limited to bolts, welds, and rivets. In a preferred embodiment of the invention, the upper airbag mount attaches to the stock shock absorber mount on the main frame.
In a preferred embodiment of the invention, the lower airbag mount is fixedly attached to the swingarm at the swingarm attachment site. In another embodiment of the invention, the lower airbag mount comprises multiple swingarm attachment sites. In a preferred embodiment of the invention, the lower airbag mount attaches to a box section near the center of the swingarm. In one embodiment of the invention, the lower airbag mount is held in place by the weight of the motorcycle. In another embodiment, the lower airbag mount is attached by one or more methods, including but not limited to bolts, welds, and rivets. In yet another embodiment of the invention, the lower airbag mount attaches to one or more stock tie-rod attachment points on the swingarm and the lower airbag mount comprises one or more alternative tie-rod attachment points.
In a preferred embodiment of the invention, the airbag suspension system comprises two tie-rods pivotally connecting the swingarm to the relay arm. In another preferred embodiment, the stock tie-rods are used.
In another embodiment of the invention, the relay arm is oriented so as to translate constant upward arcuate swingarm motion into progressively increasing linear shock absorber compression motion, thereby providing a progressive shock absorber linkage. In another embodiment, the airbag suspension system comprises an externally adjustable shock absorber. In a further embodiment, the airbag suspension system comprises a coil-over spring shock absorber.
In another embodiment of the invention the airbag suspension system provides at least one adjustment for the baseline ride height of the motorcycle. In a preferred embodiment, the adjustment is built-in to at least one of the airbag mounting sites.
In one embodiment of the invention, the airbag suspension system comprises an air compressor functionally connected to the airbag. In a preferred embodiment, the air compressor is functionally connected to the electrical charging system of the motorcycle and can be operated by a switch mounted on the motorcycle. In another embodiment, the invention further comprises a solenoid valve that allows the release of pressure in the airbag. In a preferred embodiment, the solenoid valve is functionally connected to the electrical charging system of the motorcycle and can be operated by a switch mounted on the motorcycle. In another preferred embodiment, the invention further comprises a consolidated switch assembly that allows the operator to increase and decrease air pressure to the airbag suspension system. In a most preferred embodiment, the consolidated switch assembly is handlebar-mounted. In another embodiment, the switch assembly is dashboard-mounted.
In another embodiment of the invention, the compressor is functionally connected to a pressure reservoir (e.g., a compressed air cylinder) that is functionally connected to the airbag through a second solenoid valve. In a preferred embodiment, the second solenoid valve is operated by a switch or a consolidated switch assembly mounted to the handlebar or dashboard. In another preferred embodiment, a pressure switch monitors the pressure in the reservoir and automatically operates the compressor so as maintain constant predetermined air pressure in the reservoir.
In another embodiment of the invention, the airbag suspension system further comprises an air pressure gauge functionally connected to the airbag suspension system. In a preferred embodiment of the invention, a microprocessor monitors the pressure in the airbag suspension system and alerts the operator of the motorcycle to sudden changes in the air pressure. In yet another embodiment of the invention, the microprocessor monitors the ride of the motorcycle and adjusts the air pressure in the airbag to maintain a preset ride height.